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Re: filmscanners: Scanner resolution (was: BWP seeks scanner)



In a message dated 6/15/01 11:53:29 AM Eastern Daylight Time, 
Paul_Chefurka@pmc-sierra.com writes:

<< This implies to me that the film itself is the limiting factor for "image 
sharpness".  While we might all like to see 8000 ppi scanners for a number of 
reasons, we won't actually resolve much more image content that the current 
4000 ppi models are providing.
 
 After all, 4000 ppi gives a resolution of 75 lp/mm or so, and it takes 
pretty remarkable technique to actually get that kind of resolution onto 
film.  Or is my crude first-approximation assessment incorrect, and we 
actually can't resolve detail in the scan at more than half that - say 40 
lp/mm with reasonable contrast?  Even that level is still sufficient for 
prints that appear "sharp" at normal viewing distances.
 
 Whatever the final outcome may be (once we've worked through the morass of 
differences between film and digital image reproduction technology and 
information theory) I'm still left with the feeling that current scanner 
resolution is getting off the film most of what's actually there.  An 
order-of-magnitude improvement is probably not available in this system.
 
 Paul Chefurka >>

Here is an interesting observation from Michael J. McNamara (PopPhotgraphy 
July, p58)at the conclusion of the article on their scanner tests: "...Even 
the best 4000 dpi scanners we've tested aren't capable of capturing all the 
detail found in a 35mm color original under optimum conditions (tripod, 
mirror lockup,etc). In our tests the highest res we've found in a 35mm color 
slide or negative is 77 lp/mm.  The best 4000 ppi scanner can capture about 
60 lp/mm, about 25% lower.  But that's perfect, because under normal shooting 
conditions (i.e., handheld instead of tripod mounted), 60 lp/mm is about all 
you'll ever get from an SLR."

Whatever the theoretical merits of McNamara's observations, it appears to me 
that they clearly are in agreement with the conclusions by Paul and  Raphael. 
 BTW, the 2900 ppi Nikon CoolscanIV resolved 53.3 lp/mm vs 60 lp/mm for the 
CoolScan 4000ED; does this imply that it "outperformed" the more expensive 
scanner on a relative basis?

Bruce




 




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